1. Field of the Invention
The present invention relates generally to electronic device burn-in systems and more specifically it relates to a method of controlling spray distances in a spray unit for efficiently thermally managing one or more electronic devices.
2. Description of the Related Art
Thermal management systems for electronic device burn-in equipment have been in use for years. Conventional thermal management systems utilized today are comprised of, for example, either air-cooled enclosures, or fluid-cooled cold plates. Upcoming technologies include refrigeration systems or other two-phase based technologies.
When producing electronic devices, manufacturers typically perform three different tests on the electronic devices prior to shipping: (1) sort, (2) burn-in, and (3) class testing. Sort test requires maintaining the wafers at a modest temperature, e.g. 35° Celsius, while the wafers are probed for defects. Conventional fluid-cooled cold plates are employed at this stage. Projected heat fluxes, even at the wafer sort, are pointing to the fact that a more effective thermal management technology is needed at this stage.
Burn-in of the electronic devices is typically accomplished utilizing elevated voltages and temperatures in a process that raises the junction temperatures of a batch of electronic devices. The lifespan of an electronic device is closely related to its operating temperature wherein operating under increased temperatures reduces the effective lifespan of the electronic device. By applying increased voltages and temperatures to an electronic device, the weaker electronic devices will fail during testing. The length of the burn-in of electronic devices is directly tied to the median junction temperature of the batch of electronic devices. It is therefore important to maintain a relatively narrow junction temperature spread that provides a higher median temperature. For example, a poor thermal management system can produce a junction temperature spread from 75° to 125° Celsius resulting in a low median junction temperature, longer burn-in time and higher associated burn-in costs. Modern fluid-based thermal management systems are currently able to lower the junction temperature spread to approximately 95° to 110° Celsius thereby reducing burn-in time and burn-in costs.
Class test is the final step in the testing process and is comprised of a final series of tests to validate functionality and quantify speeds. During class test, non-uniform heating of the electronic devices typically occurs. A electronic device's speed is typically derated by 0.15% for every degree Celsius rise above the target temperature (junction temperature, Tj). It is therefore important to maintain the temperature of the electronic devices relatively close to the target temperature (Tj).
Due to increasing chip heat fluxes (projected to exceed 125 W/cm2 by the year 2004), conventional thermal management systems for electronic device burn-in are reaching their cooling limits. A further problem with conventional thermal management systems is that they are inefficient, complex, costly to implement and costly to operate. A further problem with conventional thermal management systems is that the resulting junction temperature spreads result in relatively long burn-in times of the electronic device devices. Another problem with conventional thermal management systems is that they require significant amounts of power to operate.
While these devices may be suitable for the particular purpose to which they address, they are not as suitable for efficiently thermally managing one or more electronic devices. Conventional method of controlling spray distances in a spray units are inaccurate and inefficient thereby increasing the testing costs for an electronic device manufacturer.
In these respects, the method of controlling spray distances in a spray unit according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed for the purpose of efficiently thermally managing one or more electronic devices.